Indexable insert with corners with different radii

ABSTRACT

The present invention relates to an indexable cutting insert for an end mill for machining of contours in a workpiece and to a milling tool. The cutting insert is asymmetrical in respect of a line through a hole in the cutting insert. The cutting insert comprises two cutting edge portions. Each cutting edge portion comprises a substantially straight cutting edge and a curved cutting edge along respective intersecting lines between a clearance surface and a rake face. The curved cutting edges have different lengths. The cutting insert has a bottom side and a first and a second opposite corner. The second corner is defined in plane view by a radius that is greater than, preferably at least twice as great as a radius of the first corner.

The present application is a continuation of PCT/SE2004/000382, filedMar. 16, 2004.

BACKGROUND AND SUMMARY

The present invention relates to an indexable cutting insert for an endmill for the machining of contours in a workpiece, which is based onEP-B1-504 608.

An end mill is used during complicated, and severe conditions withintensely fluctuating cutting forces under heavy demands regarding themachining precision. If indexable cutting inserts are used for an endmill, it is important to place such indexable cutting inserts preciselyin relation to the tool body and to clamp the cutting insert rigidly onthe tool body.

A conventional indexable cutting insert for an end mill, see, forinstance, U.S. Pat. No. 6,149,355 and U.S. Pat. No. 5,951,121, has twocutting edges, each comprising a curved edge and a substantiallystraight edge connecting to one end thereof. In its entirety, thecutting insert has an oval shape as seen in top view. Thus, if thecutting insert is a positive cutting insert, i.e. a cutting inserthaving a leaning side, it is very difficult to precisely position thecutting insert on a tool body and clamp the same rigidly.

It is desirable to provide a durable cutting insert for a tool body.

It is desirable to provide an easy-cutting cutting insert.

It is desirable to provide a cutting insert that makes precisepositioning of the cutting insert in the tool body possible.

It is desirable to provide a cutting insert that may be clamped rigidlyin the tool body.

According to an aspect of the present invention, an indexable cuttinginsert for a milling tool is provided. The cutting insert isasymmetrical in respect of a line through a hole in the cutting insert,the cutting insert comprising two cutting edge portions, each cuttingedge portion comprising a substantially straight cutting edge and acurved cutting edge along respective intersecting lines between aclearance surface and a rake face, the curved cutting edges havingdifferent lengths, the cutting insert having a bottom side and a firstand a second opposite corner, wherein the second corner is defined inplane view by a radius that is greater than, preferably at least twiceas great as, a radius of the first corner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a milling tool in side view. FIG. 1B shows the millingtool in end view. FIG. 1C shows the milling tool in cross-sectionaccording to the line C-C in FIG. 1A. FIGS. 1D and 1E show explodedviews of feasible positions of the cutting insert in the milling body.FIG. 1F shows a holder in side view having an interior cutting insertpocket. FIG. 1G shows the holder in side view having an exterior cuttinginsert pocket.

FIG. 2A shows a cutting insert according to the present invention inplane view. FIG. 2B shows the cutting insert in end view. FIG. 2C showsthe cutting insert in side view. FIG. 2D shows the cutting insert inbottom view. FIG. 2E shows the cutting insert in cross-section accordingto the line E-E in FIG. 2A. FIG. 2F shows the cutting insert incross-section according to the line F-F in FIG. 2A.

FIG. 3A shows an alternative embodiment of a cutting insert according tothe present invention in plane view. FIG. 3B shows the cutting insert inend view. FIG. 3C shows the cutting insert in side view. FIG. 3D showsthe cutting insert in bottom view. FIG. 3E shows the cutting insert incross-section according to the line E-E in FIG. 3A. FIG. 3F shows thecutting insert in perspective view.

DETAILED DESCRIPTION

In FIGS. 1A-1E, a milling tool 10 is shown, intended to machine foremostmoulding tools for the moulding industry. The milling tool has a holderhaving a shaft 11 and a front chip-removing end 12. The end 12 has twocutting insert pockets 13, 14, each carrying a cutting insert 30according to the present invention, preferably made from sinteredcemented carbide. A clamping member or a screw 15 holds the cuttinginsert in the cutting insert pocket. The cutting inserts 30A, 30B are soplaced that one of the cutting inserts or the interior cutting insert30A in the interior cutting insert pocket 13 extends in to andpreferably past the centre line CL of the tool. This means that the toolcan bore in the workpiece. The second cutting insert or the exteriorcutting insert 30B in the exterior cutting insert pocket 14 is arrangedsomewhat at the side of the centre line CL. The active cutting edges ofthe cutting inserts are arranged so that they form a perfect semi-sphereupon rotation.

Each cutting insert pocket 13, 14 comprises a base surface 16, which hasa central threaded boring 21 in order to receive the screw 15.Furthermore, the cutting insert pocket has a front 17 and a rearshoulder 18, with the positions being related to the axial direction ofthe tool. The base surface 16 comprises two projections 19, 20, arrangedon both sides of and at different distances from the boring 21.

The axially front projection 19 connects radially outwardly to theenvelope surface of the tool and has an extension radially inwardly,approximately halfway towards the front shoulder 17. The axially rearprojection 20 connects radially inwardly to the area of the rearshoulder 18 and has an extension radially outwardly, approximatelyhalf-way in the direction towards the envelope surface. In the interiorcutting insert pocket 13, an extension of each projection 19, 20 formsan acute angle α to the centre line CL, see FIG. 1F. In the exteriorcutting insert pocket 14, an extension of each projection 19, 20 formsan acute angles s to the centre line CL, see FIG. 1G. The angle α issmaller than the angle β. Each projection 19, 20 has a substantiallyrectangular cross-section with a somewhat chamfered top side.

The cutting insert 30 that is shown in FIGS. 2A-2F fits, as has beensaid above, in both the insert pockets 13, 14. The cutting insert isasymmetrical in respect of a line through a hole 31 of the cuttinginsert. The cutting insert has in planar view a so-called eye-shape orleaf-shape and comprises two cutting edge portions, each cutting edgeportion comprising a substantially straight cutting edge 32, 33 and acutting edge 38, 39 curved in planar view along respective intersectinglines between a clearance surface 34A and a chip surface 35. The curvedcutting edges 38, 39 have different lengths. The straight cutting edges32, 33 are not parallel but form an angle to each other, convenientlybetween 4° and 20°, preferably between 6° and 15°.

The straight cutting edges connect in the direction towards oppositecutting corners 36, 37 to curved cutting edges 38, 39. The curvedcutting edges 38, 39 are both defined by radii, e.g., between 5 and 25mm. The curved cutting edge 38 coincides with a circular sector of about85° to 97° while the curved cutting edge 39 coincides with a circularsector of about 95° to 107°. The curved edges 38, 39 have radii that ina mounted state are substantially identical. The curved cutting edgecomprises at least 40% of the extension of the cutting portion. Thecurved cutting edges 38, 39 are convex in a side view according to FIG.2C. The lower part 34B of the clearance surface 34 forms an obtuse angleto the bottom side 40 of the cutting insert. The upper part 34A of theclearance surface 34 is substantially perpendicular in relation to thebottom side 40 of the cutting insert. The upper part 34A ensures thatassociated cutting edge gets a relatively good strength.

The bottom side 40 is provided with two recesses or grooves 41, 42.

Each groove 41, 42 intersects solely one of the clearance surfaces 34under the curved cutting edge 38, 39. Thus, the groove has a limitedextension transverse to the longitudinal direction of the cutting insertand is limited by an end wall 43. Said extension of the groove isgreater than 50% of the width of the base surface 40 where the recesshas been arranged. An area of the bottom side 40 remains accordinglyunaffected by the groove and therefore a feasible support surface forthe cutting insert is retained. The groove has in cross-section theshape of a truncated triangle. The groove 41 is by comparison with thegroove 42 arranged closer the hole 31, and therefore the cutting insertcan only be placed in one way in the cutting insert pocket.

The curved cutting edge gives a positive and constantly axial cuttingprocess along the entire edge.

The cutting corners may be divided in to a first or sharp corner 36 anda second or obtuse corner 37. The obtuse corner has a double function toprotect the cutting insert in the centre upon machining in solidmaterial, such as upon drilling, as well as when the cutting insert hasbeen arranged in the exterior cutting insert pocket, the corner 37 willgenerate a progressive curve, which enables variable machining of deepshoulders. The sharp corner 36 will only be of use in the exteriorcutting insert pocket 14. The obtuse corner 37 is defined in plane viewaccording to FIG. 2A by a radius R1, which is greater than, preferablyat least twice as great as the radius R2 for the sharp corner 36. Theobtuse corner 37 has a negative rake angle and slopes in the directiontowards the bottom side 40 from the rake face 35, i.e., the corner 37slopes from the rake face 35 towards a plane that coincides with thebottom side 40. The sharp corner 36 has a positive rake angle andcomprises a continuous extension of the rake face 35. The cutting inserthas an elevated central portion 44 around the hole 31. The portion 44may act as a chip breaker. The portion 44 comprises markings, where oneknob relates to peripheral mounting and two knobs means centralmounting. The corresponding markings exist at the insert pockets 13 and14.

FIGS. 3A-3F show an alternative embodiment of a cutting insert 30′according to the present invention. What distinguishes the cuttinginsert 30′ from the previously described cutting insert 30 is that thecutting insert 30′ is formed with chip breakers optimised for machiningof work materials being difficult to turn. Equal details have beenprovided with equal reference numerals. The chip breakers comprise ofrecesses 51, 52, 53 and 54 in the cutting edges 32, 33, 38 and 39,respectively.

Each recess extends down into the upper part 34A of the clearancesurface as well as also a distance into the rake face 35. As may be seenfrom the plane view according to FIG. 3A, the recesses 51, 54 and 52, 53are arranged substantially in level with the grooves 41 and 42,respectively.

The cutting insert 30, 30′ may have a chamfer along the periphery of thebottom side 40 allowing the cutting insert pocket to be formed withrelatively great radii.

The cutting insert 30, 30′ is mounted in the following way. The cuttinginsert 30A is brought towards the exterior cutting insert pocket 13 sothat the recesses 41, 42 are aligned with the projections 19, 20. In thecorrect position, the screw 15 can be inserted through the hole 31 andtightened in the boring 21.

Thereby, the bottom side 40 of the cutting insert is pressed against thebase surface 16 while three parts of the clearance surface 34B separatedfrom each other will come to abutment against the shoulders 17, 18 inthe cutting insert pocket 13. The flanks of the projections will come toabutment against the recesses 41, 42 not until upon machining providedthat the cutting insert on that occasion is allowed to move somewhat.Upon mounting of the cutting insert 30B in the interior cutting insertpocket 14, the bottom side 40 of the cutting insert is pressed againstthe base surface 16 while two parts of the clearance surface 34Bseparated from each other will come to abutment against the shoulders17, 18 in the cutting insert pocket 13. As at the exterior cuttinginsert pocket, the projections and the recesses cooperate only underload of the cutting insert 30B. Because the recess 41 intersects theclearance surface only on one side, the axially front projection 19will, upon a possible deflection of the screw, abut against the end wall43, and thereby additionally secure the cutting insert againstloosening.

Thus, the present invention relates to a durable cutting insert that iseasy-cutting and that makes precise and stable positioning of thecutting insert in the tool body possible. The cutting insert accordingto the present invention has chip-dividing properties in one embodiment.

In the present application, the use of terms such as “including” isopen-ended and is intended to have the same meaning as terms such as“comprising” and not preclude the presence of other structure, material,or acts. Similarly, though the use of terms such as “can” or “may” isintended to be open-ended and to reflect that structure, material, oracts are not necessary, the failure to use such terms is not intended toreflect that structure, material, or acts are essential. To the extentthat structure, material, or acts are presently considered to beessential, they are identified as such.

While this invention has been illustrated and described in accordancewith a preferred embodiment, it is recognized that variations andchanges may be made therein without departing from the invention as setforth in the claims.

1. An indexable cutting insert for a milling tool, the cutting insertbeing asymmetrical in respect of a line through a hole in the cuttinginsert, the cutting insert comprising first and second cutting edgeportions, each cutting edge portion comprising a substantially straightcutting edge and a curved cutting edge along respective intersectinglines between a clearance surface and a rake face and, for each cuttingedge portion, lines extending substantially perpendicularly to an axisof the hole and drawn through endpoints of the straight cutting edge andthe curved cutting edge of the cutting edge portion intersect to definean obtuse angle when viewed along the axis of the hole, the curvedcutting edges having different lengths, the cutting insert having abottom side and a first and a second opposite corner, the first andsecond opposite corners being defined by intersections between curvedcutting edges of the first and second cutting edge portions and straightcutting edges of the second and first cutting edge portions,respectively, the first and second opposite corners defining parts ofthe two cutting edge portions, wherein the second corner is defined inplan view by a radius that is greater than a radius of the first corner.2. The cutting insert according to claim 1, wherein the second cornerhas a negative rake angle and slopes from the rake face towards a planethat coincides with the bottom side.
 3. The cutting insert according toclaim 2, wherein the first corner has a positive rake angle andcomprises a continuous extension of the rake face.
 4. The cutting insertaccording to claim 3, wherein the cutting insert comprises chip breakerscomprising recesses in the cutting edges.
 5. The cutting insertaccording to claim 4, wherein the cutting insert comprises recesses in abottom side of the cutting insert.
 6. The cutting insert according toclaim 5, wherein the recesses are arranged on both sides of and atdifferent distances from the hole of the cutting insert.
 7. The cuttinginsert according to claim 5, wherein each recess intersects one of theclearance surfaces below the curved cuffing edge.
 8. The cutting insertaccording to claim 7, wherein each recess has a limited extensiontransverse to the longitudinal direction of the cutting insert and islimited by an end wall.
 9. The cutting insert according to claim 5,wherein an extension of each recess is greater than 50% of a width ofthe bottom side of the cutting insert.
 10. The cutting insert accordingto claim 9, wherein the recess in cross-section has the shape of atruncated triangle.
 11. The cutting insert according to claim 1, whereinthe curved cutting edge comprises at least 40% of an extension of thecutting portion.
 12. The cutting insert according to claim 11, whereinthe substantially straight cutting edges are not parallel but form anangle to each other.
 13. The cutting insert according to claim 1,wherein the first corner has a positive rake angle and comprises acontinuous extension of the rake face.
 14. The cutting insert accordingto claim 1, wherein the cutting insert comprises chip breakerscomprising recesses in the cutting edges.
 15. The cutting insertaccording to claim 1, wherein the cutting insert comprises recesses in abottom side of the cutting insert.
 16. The cutting insert according toclaim 15, wherein the recesses are arranged on both sides of and atdifferent distances from the hole of the cutting insert.
 17. The cuttinginsert according to claim 15, wherein each recess intersects one of theclearance surfaces below the curved cutting edge.
 18. The cutting insertaccording to claim 17, wherein each recess has a limited extensiontransverse to the longitudinal direction of the cutting insert and islimited by an end wall.
 19. The cutting insert according to claim 15,wherein an extension of each recess is greater than 50% of a width ofthe bottom side of the cutting insert.
 20. The cutting insert accordingto claim 19, wherein the recess in cross-section has the shape of atruncated triangle.
 21. The cutting insert according to claim 1, whereinthe radius of the second corner is at least twice as great as the radiusof the first corner.